An adjustable damper includes a tube body, a driving rod to be displaced in the tube body and to engage a screw sleeve to drive a screw rod and further a fixed seat for rotation. The fixed seat has a plurality of permanent magnets surrounding for circular rotation and an operation element is driven by a rotating element for repeated linear displacement; a magnetic surface is further arranged on an inner periphery of an annular element of the operation element and an annular gap is arranged between the magnetic surface and the permanent magnets; therefore the displacing annular element is able to adjust a damping force of the driving rod by adjusting an overlapped area of the permanent magnets and a magnetic surface, and further adjust an eddy load formed thereby. The damper overcomes the problem of oil leakage and ensures the durability and quality with its adjustability.